Features

• Transmitter in four-wire system with HART interface
• Housing can be mounted on 35 mm rail or 32 mm G rail
• Screw plug connector
• All circuits electrically isolated
• Output signal: 0/4 to 20 mA or 0/2 to 10 V
• Power supplies: 115/230 V AC/DC or 24 V AC/DC
• Explosion protection [EEx ia] or [EEx ib] for measurements with sensors in the hazardous area
• Temperature-linear characteristic for all temperature sensors
• Temperature-linear characteristic can be selected for all temperature sensors
• Automatic correction of zero and span
• Monitoring of sensor and cable for open-circuit and short- circuit
• Sensor fault and/or limit can be output via an optional sensor fault/limit monitor
• Hardware write protection for HART communication
• Diagnostic functions
• Slave pointer functions
• SIL 1

Mode of operation

The signal output by a resistance-based sensor (two-wire, three-wire, four-wire system), voltage source, current source or thermocouple is converted by the analog-to-digital converter (1, function diagram) into a digital signal. This is evaluated in the microcontroller (2), corrected according to the sensor characteristic, and converted by the digital-to-analog converter (6) into an output current (0/4 to 20 mA) or output voltage (0/2 to 10 V). The sensor characteristics as well as the electronics data and the data for the transmitter parameters are stored in the non-volatile memory (3).

AC or DC voltages can be used as the power supply (13). Any terminal connections are possible for the power supply as a result of the bridge rectifier in the power supply unit. The PE conductor is required for safety reasons.

A HART modem or a HART communicator permit parameterization of the transmitter using a protocol according to the HART specification. The transmitter can be directly parameterized at the point of measurement via the HART output terminals (10).

The operation indicator (4) identifies a fault-free or faulty operating state of the transmitter. The limit monitor (9) enables the signaling of sensor faults and/or limit violations. In the case of a current output, the current can be checked on a meter connected to test socket (12).

Diagnosis and simulation functions

The SITRANS TW comes with extensive diagnosis and simulation functions.

Physical values can be defined with the simulation function. It is thus possible to check the complete signal path from the sensor input to inside the control system without additional equipment. The slave pointer functions are used to record the minimum and maximum of the plant's process variable.